Every 3D product in IMVU uses a texture. In fact, the majority of IMVU 3D products are created by overriding textures.

A texture is a digital image that is applied to a 3D mesh. While textures are easier to create than a 3D mesh, those that are able to create good looking textures *and* keep their file sizes down are ninjas. All of them.

To learn how to be a ninja, please check out these tutorials:

Texture Introduction
Texture Budgets
Texture Downloads
Opacity Maps
Materials Tab